When you interact with people, you often do it on your grounds, i.e. in your area of expertise. This inherently means that you are more likely to be right in a discussion. I believe this transfers to other areas of your life – where you are not the expert. So you automatically assume you’re right even if you aren’t. However, in my experience this doesn’t apply to situations where you are very aware that you are the (intellectually) subordinate person, e.g. when talking to a doctor.